1. Field of the Invention
This invention relates to an electromagnetic control device and more particularly it pertains to a permanent magnet associated therewith.
2. Description of the Prior Art
Industrial equipment that is operated electrically, such as by a motor or industrial lighting, is usually regulated by a control device which may be a contactor or relay having parts movable between two positions for opening and closing a circuit through the motor. It is often desirable with such equipment to latch or hold the control device in an energized or "on" position for long periods of time. In the past, it has been the practice to use either a mechanical latch to jam a solenoid armature in the energized position or a permanent magnet inserted in the magnetic circuit so that upon being energized, the device remains in that position after interruption of power or until a reversal signal is applied. Moreover, a disadvantage of prior mechanical latch mechanisms has been the fact that once the coil of the solenoid is deenergized, the solenoid armature drops back a small distance until blocked by the mechanical latch. With permanent magnets of prior usage in order to obtain enough magnetic "pull" cobalt alloy magnets, such as Alnico, have been used. However, cobalt alloys are undesirable because of the uncertainty of their availability in the future and their increasing cost.